1. Field of the Invention
The present application is generally related to grinding metals and is more specifically related to systems and methods used for grinding refractory metals and refractory metal alloys.
2. Description of the Related Art
Surgical suture needles are commonly made using grinding systems having abrasive particles adapted to grind the distal ends of needle blanks into tapered points. Conventional surgical suture needles are generally fabricated from needle blanks made from non-refractory metals. Examples of non-refractory metals include stainless steel alloys such as 300 series stainless steels, and 420, 420F and 455 stainless steels.
Recently, in order to improve the strength of surgical needles, refractory metal alloys have been used in place of non-refractory metals. One preferred refractory metal alloy is a tungsten-rhenium alloy. Unfortunately, conventional grinding systems that are sufficient for grinding non-refractory metals do not work particularly well for grinding refractory metal alloys. This requires grinding wheels to be continuously replaced which adds expense and variability to the final product that is produced and which slows down the manufacturing process.
One desirable characteristic of a good grinding system includes providing a grinding wheel having a long grinding life, typically useful for grinding at least 50,000 needles. However, when conventional grinding systems are applied to needles made from refractory metal alloys such as tungsten-rhenium alloys, it has been observed that grinding wheel life is extremely short (e.g., 500-8,000 needles).
Grinding wheel failure may be due to “gumming” and/or “capping” of the abrasive material, whereby the material being ground coats the abrasive particles thereby diminishing the ability of the abrasive particles to cut the workpiece. Adding a lubricant to the grinding process has been found to reduce “gumming” and/or “capping,” which increases the life of a grinding system. However, this method introduces a new failure mode, commonly referred to as abrasive breakdown or abrasive pull-out, which leads to decreased wheel life and is a major challenge when grinding metals.
The binding material used for binding abrasive particles to a grinding tool, such as a grinding wheel, typically has a thickness that is about 50% of the average size of the abrasive particles. It is conventionally accepted by those skilled in the art that increasing the thickness of the binding material layer above 50% of the size of the abrasive particles will decrease the life of a grinding wheel due to there being less space available between the abrasive particles to accommodate the ground-off portions of the needle. Therefore, increasing the thickness of the binding material layer above 50% of the average size of the abrasive particles has been avoided by those skilled in the art.
In spite of the above advances, there remains a need for improved systems, devices and methods for more economically and efficiently grinding metal objects, such as surgical needles, made from refractory metals and refractory metal alloys.